This record-breaking prototype aircraft features twin fuselages, a straight wing cruciform profile, six engines – and a wingspan wider than the 100 m dash is long.
As large aircraft go, this one goes straight to the top of the list.
Nicknamed ‘Roc’, after the bird of Arabian mythology which could carry large animals in its grasp, the Scaled Composites Model 351 Stratolaunch is a prototype air-launch-to-orbit carrier – a mothership aircraft designed to launch hypersonic and aerospace vehicles from immense heights.
At almost 227,000 kg without a payload, and capable of carrying a maximum weight of 250,000 kg, it is also the world’s heaviest aircraft following the destruction of the Antonov An-225 Mriya during the Russian invasion of Ukraine in 2022.
8 key features of the Roc
- 6 total engines
- 117 m total wingspan
- 590 t take-off weight
- 28 wheels
- 15 m tail height
- 30 m gap between its twin fuselage
- 226,800 kg weight when empty
- 250,000 kg payload maximum weight
The craft was developed by Scaled Composites for the American company Stratolaunch Systems in 2017.
Stratolaunch Systems was founded in 2011 by Paul Allen, the billionaire who also co-founded Microsoft, and now conducts test flights out of its base in the Mojave Desert, California.
The first test flight for Roc was conducted in 2019, during which time the aircraft reached a maximum speed of 165 kt and a maximum altitude of 15,000 ft. The flight lasted almost 2.5 hours.
The aircraft configuration has been in development for two decades. It was the third aircraft of this configuration from Scaled Composites, which had previously developed White Knights One and Two (also of a mothership design) in the 2000s.
Dr Sonya Brown MIEAust, Associate Professor in Aerospace Engineering at UNSW, told create the dual-fuselage design and extremely long wing, more than simply being distinctive visual features, serve a clear functional purpose.
“This aircraft is designed as an air-launch platform, and when launching something in mid-air, ideally you want the structure of your aircraft to be as symmetrical as possible, particularly considering the large mass,” she explained.
“Air launches have taken place from the wing of a Boeing 747, for example, which is appropriate for smaller payloads, but the larger the object you wish to test, the greater the benefit of launching off the aircraft’s centreline – which is essentially the centre of gravity and mass. This helps with flight stability during the launch, which is really important for safety.
“So it’s definitely an interesting design, but it’s built around that mission of how to safely air-launch items for testing.”
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It’s not only the wingspan that stood out to Brown.
“Towards the nose of the two fuselages, there’s a regular rounded section like that in other aircraft,” she said. “But as we move back along the fuselage, we can see a more rectangular design with rounded corners.
“A rounded rectangular fuselage is not ideal for pressurisation. If you wanted pressurisation with this shaped fuselage, you’d need a much stronger structure, which makes it heavier.
“The more circular section towards the front has been done to ensure pressurisation for pilots and air crew, while the rest of the plane interior stays unpressurised.”
Brown’s personal design philosophy is that the “ideal” aircraft design is entirely mission-dependent.
“Let’s take the Stratolaunch’s wide wingspan, for example. This technically increases your aspect ratio and does have benefits in terms of the efficiency of the wing – it can bring the craft to higher lift-to-drag ratios.
“When we think about commercial aircraft that people fly on every day, however, there are limitations to the design, which is affected by standard airport layouts, passenger boarding and alighting rates, and other factors.
“But a specially designed mission aircraft such as Stratolaunch can achieve a longer wingspan because it doesn’t have to fly in and out of busy commercial airports multiple times a day and be impacted by those considerations.”
Previously in create, Brown judged the viability and efficiency of nine innovative passenger aircraft designs, including a plane with three wings and one designed to look like a bird. Watch the video below to learn which would earn carbon emissions savings.
Local projects
Large aircraft such as the Roc, the Antonov, the Airbus A380 or even the World War II-era Hughes H-4 Hercules (an entirely wooden prototype plane nicknamed the ‘Spruce Goose’) are typically the domain of other countries, with Australia’s manufacturing area of expertise being in aircrafts of a smaller size.
“With the right funding, a company such as Boeing, which does have some development in this country, could implement a new aircraft manufacturing project, but there’s nothing publicly available right now,” Brown said. “Aircraft design and development is a very expensive process. It takes many years and many millions or billions of dollars.
“The small-aircraft space is where innovative development is taking place, however.”
She pointed to examples such as the following Australian-based innovations in aerospace design and manufacturing:
- AMSL Aero’s hydrogen-powered, vertical take off and landing design Vertiia
- Boeing’s Australian arm has developed the MQ-28 Ghost Bat, or ‘Loyal Wingman’
- Western Australian-based Innovaero’s drone development, together with BAE Systems, for the Defence industry
Explore the frontiers of aerodynamics and aerostructures at next year’s Australian International Aerospace Congress.
